Several of the steps in the preparation of silicon devices for the semiconductor industry require contacting a silicon wafer with various solutions such as photoresist solvent, etching solutions and the like. These solutions must be completely removed to reduce the danger of contamination of the wafers. Distilled water rinsing is generally used, followed by a drying step. The usual drying step includes rinsing the wet device with volatile organic solvents or solvent mixtures, which displace the water and evaporate.
Several organic solvent mixtures are known and are readily available. For example, azeotropic mixtures of trichlorotrifluoroethane with solvents such as methylene chloride, methanol, ethanol, acetonitrile, acetone, hexafluoroacetone and hydrogen fluoride are disclosed in U.S. Pat. Nos. 3,400,077, 3,490,739, 3,728,268 and 3,789,004. Various azeotropic mixtures of tetrachlorodifluoroethane with water, ethanol, isopropanol, the butanols, tertiary amyl alcohol, 1,2-dichloroethane, trichloroethylene, nitromethane, acetic acid, propionic acid, dioxane, isopropylacetate, monomethyl ether of ethylene glycol and the like are disclosed in U.S. Pat. Nos. 3,530,073, 3,554,918, 3,640,884, 3,671,442, 3,671,443, 3,671,444, 3,671,446, 3,692,686, 3,694,368, 3,729,424, 3,785,987, 3,794,590 and 3,836,474. However, the presence of chlorine in these polyfluorinated compounds results in the formation of hydrochloric acid in aqueous solution which adversely affects silicon devices. Further, since the above chlorofluoro compounds are not good wetting agents, a surfactant is usually added, which also increases the danger of contamination of the silicon wafer.
Volatile solvents such as acetone can also be employed as drying agents, but acetone has a very low flash point (15.degree. F. or -9.degree. C.) and thus it constitutes a fire hazard and can not be used in commercial operation.
Aqueous isopropanol mixtures are excellent wetting agents, and do not contaminate silicon surfaces, but since they are not volatile, devices must be blown dry to remove the last of the liquid, adding an additional step and expense to manufacture.
It would be highly desirable to obtain a volatile, non-flammable, azetropic mixture which does not contain chlorine, and which can dry silicon devices without contaminating them.